The invention relates to the field of ellipsometry, and more particularly to spectroscopic ellipsometry.
It finds a general application in any field in which ellipsometry is used, and more particularly in micro-electronics in the optical inspection of a laser surface treatment, such as the annealing of amorphous silicon samples by excimer laser. It thus finds a very particular application in the manufacture of liquid crystal screens consisting of at least one layer of amorphous silicon deposited on a transparent substrate. It also finds an application notably in surface cleaning, polishing and preparation.
In the patent FR-A-2602338 and in the article: JOURNAL OF APPLIED PHYSICS, Aug. 1, 1986, US, vol. 60, No. 3, ISSN 0021-8979, pages 859-873, XP00579985, M. ERMAN et al, "Spatially resolved ellipsometry"; an ellipsoneter comprises in general terms a light source, a sample holder, a photodetector, a first optical system mounted between the light source and the sample holder, and a second optical system mounted between the sample holder and the photodetector. The first optical system illuminates the sample supported by the sample holder, at an oblique angle of incidence, by means of a polarized light beam. The second optical system collects the light sent back by the sample. In practice, first focusing means, associated with the first optical system, focus the illumination beam coming from the said first optical system on the sample whilst second focusing means, associated with the second optical system, focus the beam reflected by the surface of the sample on the entrance of the second optical system.
In the patent application entitled "Device and method for laser surface treatment", filed by the Applicant under the number 95 09778 and published under the number FR-A2737806 (for all useful purposes, the content of this application forms an integral part of the present application), a characterization of a sample by ellipsometry is advantageously used in the manufacture of liquid crystal screens, in order to optimize the process of recrystallization of the silicon by laser by controlling the application of the laser energy by means of the ellipsometry measurement.
In such a manufacture of liquid crystal screens, the sample holder supports a sample comprising at least one layer of a material of the amorphous silicon type, of given thickness and deposited on a transparent substrate (for example glass) of given thickness. The front face of the sample receives here the illumination radiation whilst the rear face of the sample is in contact with the sample holder.
Because of the thickness of the transparent substrate, the interface between the rear face of the said sample and the sample holder reflects towards the second optical system and the photodetector an interference light beam which may falsify the ellipsometry measurements.